Process for removal of radioactive contaminants



United States Patent O 3,033,794 k PROCESS FOR REMOVAL OF RADIOACTIVE CGNTAMINANTS Frank G. Morris, Spokane, Wash, assignor, by mesne assignments, to Purex Corporation, Ltd., a corporation of California No Drawing. Filed July 23, 1956, Ser. No. 599,342 7 Claims. (Cl. 252-435) This invention relates to the decontamination of surfaces on which are deposited radioative materials, and is especially concerned with a novel composition and process for radioactive decontamination of the clothing of personnel handling radioactive materials.

In the manufacture and handling of radiaactive materials, the equipment used in processing and the clothing of workers become contaminated with the radioactive materials to a degree Where it becomes a health hazard to personnel. In the past, many such contaminated articles have been discarded because of uneconomical or impossible cleaning requirements. To alleviate this costly procedure, considerable research has been carried out on processes and compounds that will economically remove the radioactive contamination.

It has been known to employ a glassy phosphate in an efiort to remove radioactive contamination from workmens clothing. It has also been known that sodium carbonate may be somewhat effective in the removal of radioactive contamination. These materials have been used either alone or in combinations with cleaning aids such as soaps and synthetic detergents. Also, other inorganic phosphates, inorganic silicates, citric acid and bentonite clays have been employed. None of these materials, however, used either alone or in combination have proven entirely effective. In many instances, even repeated cleaning with the same reagent Will not reduce the level of radioactivity below the point of safety.

In copending application Serial No. 536,297, filed September 20, 1955, by Elmer L. Brevik, there is disclosed a active contamination from surfaces, and to eliminate steps employed in conventional processes utilizing known compositions.

Other objects and advantages will be apparent from the following description of my invention.

I have found that a composition essentially comprising a polyphosphate, a nonionic or an anionic detergent, and a monohydroxy aliphatic monocarboxylic acid of from 2 to 3 carbon atoms, when used in a water solution, is

highly effective in the removal of radioactive contami- 3,033,794 Patented May 8, 1962 ice moval of radioactive contaminants emitting beta-gamma radiation.

The polyphosphates which I have found to be etfective are the water-soluble crystalline polyphosphates and the water-soluble amorphous polyphosphates commonly called glassy phosphates, the glassy phosphates being preferred.

Representative water-soluble v crystalline polyphosphates which I employ are the alkali metal or ammonium pyrophosphates of the empirical formula M P O tripolyphosphates of the empirical formula M 1 0 and trimeta phosphates of the empirical formula M (PO and the acid salts of the above noted polyphosphates, such as M H P O and M3HP2O7, wherein M is an alkali metal such as sodium or potassium, or ammonium.

Glassy phosphates have been defined in the literature as condensed phosphates having a Na O:P O ratio of from 0 to 1.7. The phosphate glass with a mol ratio of 1.0 has been called Grahams salt, and sometimes referred to as hexametaphosphate of the formula (MPU The degree of polymerization of these glassy phosphates or polyphosphates is determined from their approximate analysis. See Properties of the Chemistry of Phosphorus, John R. Van Wazer, Interscience Encyclopedia, Inc., 1953.

The glassy phosphates employed in my invention are; polyphosphates which have a M O:P O ratio of about 0.9 to about 1.3, M being an alkali metal'such as sodium or potassium, or ammonium. The term glassy phos;

phate is employed herein to denote and include any or all of these materials. Preferably, the glassy phosphates which I employ are those 'which when dissolved in water-- in a concentration of about 31 grams per liter of solution give a pH of from about 6 to about 8.

When the polyphosphates preferably employed are sodium polyphosphates such as sodium tripolyphosphate and sodium hexametaphosphate, and the equivalent alkali metal, e.g., potassium, polyphosphates and the equivalent ammonium polyphosphates, mixed alkali metal polyphos phates can also 'be employed. Thus, for example, the. polyphosphates of sodium in which the sodium cation is j partially. substituted with potassium or ammonium can be Y anhydrous composition, although it is understood that in certain instances larger or smaller amounts of this material can be utilized.

The detergent ingredient of my composition should be a non-ionic or an anionic detergent, the non-ionic type being preferred. The non-ionic and anionic detergents. useful in the invention are deemed to be those which are chemically stable in acid solutions having an acidity between pH 3 and 7. Mixtures of these two types of detergent can also be employed. Illustrative examples of nonionic and anionic detergents useful for purposes of the invention are listed in Tables 1 and 2 below, but it is to be understood that these are only materials which can be used.

examples of many of these Sodium-ethylherane Anionic Detergent Carbide dz Carbon Chem- Tergltol EH; sulionate. icals Corp. Alkyl aryl sulionate Nacconol Aigcd Chemical dz Dye orp.

Na Salt of alkyl aryl Bohm & Haas Co. 7

Triton 770 poly-ether sulfate.

Nonic 300 has the following properties:

Appearanceclear, pale straw color Cloud point(l.% aqueous solution)'56 C. Specificgravity-20l20 C.1..06

Ninol' 2012 is a diethanolamide condensation product of coconut fatty acid in which two mols of di'ethanolamine j are condensed with one mol of fatty acid.

Sterox SK is ethoxylated' alkyl thio ether having the following properties:

Pour point-.55 F.

Teox 12 has the following formula:

R-i Z-O.(C2 .4O)iiwhere R is 312111 oil acid. a

Tr'itonX-l-OO has the following. formula: on; r on,

cn -d-om-h-gtcinio) ,-on

where x is from about 9 to about 10. I i V Tween '21 is sorbitan monolaurate which has been ethoxylated at the non esten'fied hydroxyls with'ethoxy chains of variable lengths.

Tergitol EH is sodium Z-ethyl hexyl sulfate of the formula v CH CH;-OHi-.CH==C CHrSOaNa Naccr'mo'l is an alkyl benzene sultonate of the formulae some where R is an alkyl group having from about 12 to about 18 carbon atoms.

The amount of detergent component in my composition is preferably between 1% and by weight of the anhydrous composition, although larger or smaller quantities on occasion maybe employed.

--The third essential ingredient of mono hydroxy aliphatic monocarboxylic acid such as hydroxy acetic acid, lactic acid, or'mixtures thereof, hy-

droxy acetic acid being preferred. The amount of the hydroxy acid component employed'is preferably from 5% to 50% by weight of the anhydrous composition, although again, as in the case of the polyphosphate and detergent components of my composition, the amount of the hydroxy aliphatic 'acid employed may be increased or demy composition is a 4 creased above and below'the aforementioned range in some cases.

In formulating the compositions of my invention, I may mix together the ingredients, for example, alkali metal polyphosphate, non-ionic detergent, and hydroxy acetic acid, to form a single composition which can be packaged and when ready for use, added to water. If desired, however, the ingredients may be separatelydissolved in water to give the solutions described below.

It is believed that a synergistic action takes place between the three above noted components of my composition when employed in aqueous. solution, which gives results superior to and unexpected from, compositions corn tainingonly one or two of the ingredients of my comthis purpose.

position, as regards efiectiveness for removal of'radioactive contamination, especially contaminants emitting alpha rays such as uranium and plutonium. However, I desire it to be understood that the invention is not to be limited by any theory as to the manner in which the components of my composition function.

The invention composition when dissolved in water forms a solution having a pH range of between about 3 and about 8, the preferred compositions with the range of ingredients noted above having a pH of between about 3.5 and about 5.5. It will be noted then that the pH of my solutions is generally slightly on the acid side in contrastto the alkaline solutions conventionally employed for The concentration of the anhydrous composition in the solutions can vary, a range of about '1 to about 8 ounces or more per gallon ofsolut ion being satisfactory, with a" proportion of about 2 to 5 ounces per gallon preferred.

If desired, small amounts of other materials which do not. afiect the functioning ofthe main ingredients of my composition for removal of radioactive contamination, can be added to the compositions or solutions of the invention, e.g., small amounts of cationic detergents and small amounts of: materials usually associated as impurities with the essential components of my composition, such as sulphates and chlorides. However, these additional materials are not essential to the invention.

In normal commercial laundering operations, the fiber of the materials being laundered is cleaned by strong aikalies followed by a subsequent acid sour, the purpose of the sour being to remove all alkalinity so that the clothing in contact with the skin will not cause irritation of the skin. The composition and process of my invention, inaddition to their effectiveness for removal of radioactive contamination, have the added advantage for laundering purposes of not requiring a subsequent acid sour, since my composition in water solution produces a pH generally slightly on the acid side or sufficiently close to neutral, as indicated above, to avoid this additional step. At the pH of my solutions, which is in the vicinity of the pH of said acid sours, the cleaning solution will produce no irritating effect on the skin even if the fiber is inadequately rinsed. This advantage materially reduces the time of the operation and eliminates the need for the add sour, resulting in additional economy of operation.

The tests on removability of radioactive contamination according to my invention were conducted on three types of radioactive sources, namely: uranium, plutonium, and soft beta radiation emitters. The-plutonium was tested for removability of alpha radiation, the uranium for removal of alpha and the combination of beta and gamma rays, and the soft beta for removal ofmaterials emitting the combination of beta-gamma rays. The materials emitting beta and gamma rays were included as one category because the counting devices determined the radiation level of both these products. The results of these tests showed removal up to 99% of contaminants emit-ting alpha rays Thetests were conducted in a Washer or container con stnuctcd of stainless steel. In no instance was a redeposition of the radioactive emitters noted, indicating effectiveness of the invention composition and process for the removal of contamination from metal as well as clothing. The invention composition may also be elfective in the removal of radioactivity from other types of surfaces such as concrete, rubber, canvas and wood." Temperatures of the laundering operation are those conventionally employed, e.g., from 120 F. to 180 F.

The following examples serve to illustrate the invention: I

EXAMPLE 1 A composition according to the invention was added to water in a concentration of 2.6 ounces of the anhydrous composition per gallon of water. The pH of the solution was about 4. The composition consisted of the following ingredients:

Composition Y: Percent by weight Sodium hexametaphosphate 70.2

Alkylarylpolyether alcohol (Triton X-l00) 2.3 Alkyl aryl sulfonate (Nacconol) 5.3 Hydroxy acetic acid 22.3

The solution was tested on patches of cotton cloth contaminated with radioactive substances.

The test patches were contaminated with three known contaminants, namely, radioactive products of uranium and of plutonium, and material emitting soft beta rays. The uranium products emit alpha and beta-gamma rays, plutonium emits alpha rays and the soft beta emits betagamma radiation. The composition of the materials emit-ting soft beta rays Was unknown. The cotton patches were subjected to a minute wash in the solution at about 180 F. containing Composition Y and were then rinsed. Thereafter, the patches were dried in hot air dryers at about 180 F. The water used was tap water of 4.4 grains hardness.

Following treatment of the patches as described above, the contaminants remaining thereon were tested at three levels, arbitrarily chosen by the degree of emission. The low level contamination for beta and gamma emitters started at 400 counts per minute; the highest level of contamination for beta and gamma emitters was 40,000 counts per minute with the intermediate level approximately half Way between. The alpha contamination derived from plutonium and uranium also started at 400 counts per minute with the high level contamination at 4,000 counts per minute and the intermediate approximately 2,000 counts per minute.

The results of a number of tests employing the above composition and precedure are as follows:

A second composition according to the invention was added to water in a concentration of 3.4 ounces of the anhydrous composition per gallon. The pH of the solution was about 4. The composition consisted of the following ingredients:

Composition Z: Percent by weight Sodium hexametaphosphate 58.3 Alkylmylpolyether alcohol (Triton X-100) 20.0

Alkyl aryl sulfonate (Nacconol) 4.2 Hydroxy acetic acid 17.5

Tests similar to the tests of Example 1 were carried out using the same procedure, but employing Composition Z instead of CompositionY.

The results obtained were as follows:

Percent Removed 2 Contaminant Alpha Beta- Gamma Plutonium 96 Uranium 92 88 Soft Be 91 described above for radioactive contamination. The results obtained were as follows:

Percent Removed Contaminant Alpha Beta-Gamma Plutonium 99 Uranium -L- 98 100 Soft Beta It is seen that excellent removal of piutonium alpha" and of both uranium alpha and beta-gamma took place, with fairly satisfactory removal of soft beta emitters.

EXAMPLE 4:

Results similar to those of Examples 2 and 3 are ob tainable by omitting the anionic alkyl aryl sulfonate de-v tergent from Composition Z and replacing it with a like amount of the all iylarylpolyether alcohol non-ionic detergent or with a like amount of the hydroxy acetic acid.

EXAMPLE 5 Results similar to those of Examples 2 and 3 can be obtained by replacing the sodium hexametaphosphate of Composition Z with a like amount of sodium polyphosphate having a Na O:P O ratio of 1.2.

' EXAMPLE 6' Similar results to those of Examples 2 and 3 may be obtained by replacing the hydroxy acetic acid of Composition Z with a like amount of lactic acid.

EXAMPLE 7 Results comparable to, but not quite as efiective as, those of Examples 2 and 3 are obtainable by replacing the sodium hexametaphosphate of Composition Z with a like amount of sodium tripolyphosphate or sodium pyrophosphate.

Comparative tests for removal of radioactive contaminants were run employing solutions according to the invention and prior art solutions, e.g., those containing a polyphosphate, sodium carbonate, trisodium phosphate and soap. In general, the invention composition containing a polyphosphate as above described, a nonionic or anionic detergent, and hydroxy acetic or lactic acid, was superior in efiectiveness to conventional laundering compositions and processes known for this purpose.

The laundering operation according to the process of the invention, preferably employing my polyphosphate, non-ionic detergent and hydroxy acetic acid composition, moreover has the advantage of being in the nature of a 7 normal cleaning or laundering procedure withthe important and economicalexception that it is not necessary to use the conventional acid sour and numerous rinses after cleaning. The invention composition is preferably slightly acid or almost neutral when dissolved in water and will therefore notproduce chapping or skin irritation from retained alkalinity 'on the surfaces of the V clothing, which is so noticeable with the highly alkaline compounds'formerly used in laundry operations for radioj active decontamination purposes. of the invention do not produce undesirable corrosion of Further, the solutions surface with a solution in water of a composition which consists essentially of a water soluble polyphosphate of the group consisting of alkali metal and ammonium poly phosphates, a detergent of the group consisting of nonionic and anionic synthetic, detergents stable in acid solutions of a pH of 3 to 7, and a monohydroxy aliphatic monocarboxylic acid of the group consisting of hydroxy acetic acid and lactic acid, the range of ingredients in said composition being20% to 80% polyphosphate, l% to detergent, and 5% to 50% hydroxy acid.

2. 'A process effective for removal of radioactive contaminantsfrom a surface,.which comprises treating said surface with a solution in Waterof a composition which consists essentially of a polyphosphate having a M O:P O ratio of about 0.9 to about 1.3,'M being a member of the group consisting of alkali metal and ammonium, a nonsoap detergent of the group consisting of non-ionic and anionic synthetic detergents stable in acid solutions of a pH of 3 to 7, and a monohydroxy aliphatic monocarboxylic acid of the group consisting of hydroxy acetic acid and lactic acid, the range of ingredients in said composition being 20% to 80% polyphosphate, 1% to 25% detergent, and 5% to 50% 'hydroxy acid.

3. A process efiective for removal of radioactive 'contaminants emitting alpha radiation from a surface, which comprises treating said surface with a solution in water 8 consisting essentially of an alkali metal polyphosphate having a M O:P O ratio of about 0.9 to about 1.3, M being an alkali metal, a non-ionic detergent and hydroxy acetic acid, the range of ingredients employed by Weight of the mixture of ingredients being as follows: 20% to 80% polyphosphate, 1% to 25% detergent and 5% to hydrox-yacid. '1

4. Aprocess as 'definedlin'claim 3., wherein said alkali metal is sodium.

5'. A process as defined in claim .4, said solution including an anionic nonsoap synthetic detergent stable in acid solutions of a pH of 3' to 7, said 1% to 25% of detergent including both said nonionic and said anionic detergents.

6. A process effective for removal of radioactive contaminants including uranium and plutonium from clothing, which comprises treating said clothing with a solution in water consisting essentially of a water soluble polyphosphate which when dissolved in Water in a concentration of about 31 grams per liter gives a solution having a pH of about 6 to about 8, a non-ionic detergent and hydroxy acetic acid, the range of ingredients employed based on the total weight of said ingredents being as follows: 20% to polyphosphate, 1% to 25% detergent, and 5% to 50% hydroxy acetic acid.

7. A process as defined in claim 6, wherein said polyphosphate is sodium hcxametaphosphate.

References Cited in'the file of this patent UNITED STATES PATENTS OTHER REFERENCES Elder et aL: Surfactants in Shampoo Formulations, Drug and Cosmetic Industry, November 1955, 77, 5, page 714.

Snell: Soap and Sanitary Chemicals, October 1953, pages 42-44. 

1. A PROCESS EFFECTIVE FOR REMOVAL OF RADIOACTIVE CONTAMINANTS FROM A SURFACE, WHICH COMPRISES TREATING SAID SURFACE WITH A SOLUTION IN WATER OF A COMPOSITION WHICH CONSISTS ESSENTIALLY OF A WATER SOLUBLE POLYPHOSPHATE OF THE GROUP CONSISTING OF ALKALI METAL AND AMMONIUM POLYPHOSPHATES, A DETERGENT OF THE GROUP CONSISTING OF NONIONIC AND ANIONIC SYNTHETIC DETERGENTS STABLE IN ACID SOLUTIONS OF A PH OF 3 TO 7, AND A MONOHYDROXY ALIPHATIC MONOCARBOXYLIC ACID OF THE GROUP CONSISTING OF HYDROXY ACETIC ACID AND LACTIC ACID, THE RANGE OF INGREDIENTS IN SAID COMPOSITION BEING 20% TO 80% POLYPHOSPHATE, 1% TO 25% DETERGENT, AND 5% TO 50% HYDROXY ACID. 